In an attempt to move this blog to a more highbrow, or at least academic status, I’d like to point out a research paper by two Cornell University scientists, Benjamin K Tippett and David Tsang. Titled[inlinetweet prefix=”” tweeter=”” suffix=””] Traversable Achronal Retrograde Domains In Spacetime[/inlinetweet], it is a fascinating contemplation of some spacetime geometries that could be used for time travel. Science is important to me and I’m currently inspired by Simon Guerrier and Marek Kakula’s Scientific Secrets of Doctor Who.

The paper’s abstract is:

There are many spacetime geometries in general relativity which contain closed timelike curves. A layperson might say that retrograde time travel is possible in such spacetimes. To date no one has discovered a spacetime geometry which emulates what a layperson would describe as a time machine.
The purpose of this paper is to propose such a space-time geometry. In our geometry, a bubble of curvature travels along a closed trajectory. The inside of the bubble is Rindler spacetime, and the exterior is Minkowski spacetime. Accelerating observers inside of the bubble travel along closed timelike curves. The walls of the bubble are generated with matter which violates the classical energy conditions. We refer to such a bubble as a Traversable Achronal Retrograde Domain In Spacetime.

The paper is available free on the Cornell University Library website: Traversable Achronal Retrograde Domains In Spacetimeand astute readers will note the paper was published just before the 50th anniversary, so it’s taken a while to come to light! A simpler version of the paper, for lay readers is available at: The Blue Box White Paper. The synopsis for that paper is as follows:

[pullquote]Before we begin, would you like a Jelly Baby?[/pullquote]

This white paper is an explanation of Ben and Dave’s TARDIS time machine, written for laypeople who are interested in time travel, but have no technical knowledge of Einstein’s Theory of General Relativity.
The first part of this paper is an introduction to the pertinent ideas from Einstein’s theory of curved spacetime, followed by a review of other popular time machine spacetimes. We begin with an introduction to curvature and lightcones. We then explain the Alcubierre Warp Drive, the Morris-Thorne wormhole, and the Tipler cylinder.
We then describe the Traversable Achronal Retrograde Domain in Spacetime (TARDIS), and explain some of its general properties. Our TARDIS is a bubble of spacetime curvature which travels along a closed loop in space and time. A person travelling within the bubble will feel a constant acceleration. A person outside of the TARDIS will see two bubbles: one which is evolving forwards in time, and one which is evolving backwards in time. We then discuss the physical limitations which may prevent us from ever constructing a TARDIS.
Finally, we discuss the method through which a TARDIS can be used to travel between arbitrary points in space and time, and the possible dangers involved with exiting a TARDIS from the wrong side.
Before we begin, would you like a Jelly Baby?